Plate heat exchangers are well known devices for the transport for heat between two different media, in particular fluids. Such plate heat exchangers usually comprise a plurality of heat exchanger plates, wherein each heat exchanger plate comprises a pattern of indentations as well as inlets and outlets for the two media. Each pair of neighboring plates is joined in such a way that channels for the transport of the separate media are created. The two media will then be allowed to circulate between alternating pairs of plates to allow a transfer of heat through the heat exchanger plates. The pattern of indentations of one plate will be in contact with the indentation patterns of the two neighboring plates. This way the plates are kept slightly spaced and the shape of the fluid path can be adjusted to improve the efficiency of the heat exchange.
In the state of the art, it is common to use a so called herringbone pattern of indentations comprising ridges and valleys that force the flow of the media to accelerate and decelerate repeatedly within the plane of the heat exchanger plate. This usually leads to a large variation of the speed, or flow rates, of the fluids which reduces the effectiveness of the heat transfer. Thus, a pattern of indentations that allows for a more homogeneous speed of the fluids would be beneficial.
In order to improve the efficiency of the heat exchange, it has been tried to reduce the surface area used as contact surface of the neighboring heat exchanger plates or to reduce the thickness of the heat exchanger plates. Both measures may be problematic because they reduce the durability of the heat exchanger plates. In particular the high fluid pressures as well as for some cases the external pre-tension will expose the contact surfaces of the heat exchanger plates with large forces. Thus, if the contact areas of the heat exchanger plates and/or the thickness of the heat exchanger plates are too small, these forces can lead to permanent deformations of the heat exchanger plates.
In U.S. Pat. No. 8,091,619 B2 a heat exchanger of the type mentioned above is disclosed. Therein the herringbone pattern of indentations is replaced by a plurality of dimples, comprising tops and bottoms. The flat tops of one plate are brazed together with the flat bottoms of a neighboring plate. Thus, the stability of such a brazed heat exchanger can be improved allowing to reduce the thickness of the heat exchanger plates. At the same time the surface area at which the two neighboring plates meet is optimized. Thus the efficiency of such a plate heat exchanger is improved.
Such a construction has the disadvantage that the fluid flow is harder to direct and distribute across the whole plane of the heat exchanger plate. This is one reason why such heat exchangers and those having e.g. herringbone patterns, has relative slim and long designs, this reducing the width to which the fluids is to flow.
For herring bone exchangers with wedge shaped flow channels, the higher the angle of the wedge shape the lower pressure drop seen in the width direction (orthogonal to the overall flow direction seen from inlet to outlet) and higher drop in the overall flow direction, whereas by making a more narrow wedge shape with a smaller angle the pressure drop in the width direction increases whereas the pressure drop in the overall flow direction decreases. This including the height and slope of the sides of the corrugations in herringbone patterns are the parameters that may be changed to obtain a given desired flow/pressure characteristic of the heat exchanger. Increasing the width of the channels by increasing the top surface area of the patterns would reduce the total heat exchange surface and this is not a desired option. Changing one parameter to obtain a desired pressure/flow/speed characteristic thus compromises another.
Further disadvantages especially for embodiments with gasket heat exchangers, where the plates are connected and fixed together such as by bolts, and where gaskets at the circumference seals the flow channels, is related to the height of the plates, being the height from top to bottom. It may be an advantage for such heat exchangers, given a certain length and width, to be able to use the same gaskets despite the height of the actual design, as this would lower production costs. With the pattern design from U.S. Pat. No. 8,091,619 B2 it may not be possible to design plates with larger height still maintaining the desired pressure drops of the fluids within.